Just curious but what is the desire for all that rubber out back? I ask because you mention wanting the rear end to be lively under boost. With those steamrollers out back and the much longer gears of the 930 trans you are going to need lots more HP to turn those things over.

When I bought my car it had 315's on 11.5'' wide wheels. It looked awesome but I never realized how much they drug the car down until I drove it with the factory wheels on it. The car was much easier to get out of the hole, shifted smoother, made boost quicker and was much punchier at Interstate speeds.

I think if you want something fun to drive on the street you are looking at too much tire.